In one form of ion implantation apparatus, wafers for treatment are mounted at a number of discreet positions around the periphery of an implant wheel. The wheel is mounted at the free end of a scanning arm which is mounted at its other end for reciprocating motion about a scanning axis. The scanning arm and implant wheel are located in a vacuum chamber to which a beam of desired ions is directed from an ion source. As the wheel rotates at the end of the scanning arm, the various wafers mounted around the periphery of the wheel are brought successively in front of the beam. At the same time, the scanning arm more slowly moves the axis of rotation of the wheel to and fro, so that the ion beam is progressively scanned over the whole surface of the wafers.
Apparatus of this kind is known from U.S. Pat. No. 4,733,091 and U.S. Pat. No. 4,899,059.
In U.S. Pat. No. 4,733,091, the scanning arm of the apparatus is mounted for reciprocating movement by means of a rotary vacuum seal on the scan axis of the scanning arm. The implant wheel is driven by means of drive shafts and belts from outside the vacuum chamber, with the drive belts extending the length of the scanning arm to drive the shaft of the implant wheel rotatably mounted at the free end of the scanning arm.
In U.S. Pat. No. 4,899,059, the implant wheel is driven directly by an electric motor mounted at the end of the scanning arm within a sealed housing inside the vacuum chamber. The scanning arm of the '059 patent is mounted for reciprocating motion about an axis located outside the vacuum chamber. This scan axis is parallel to the adjacent wall of the vacuum chamber so that a bellows-type seal is necessary between the scanning arm and the wall of the vacuum chamber through which it extends, in order to accommodate the movement of the scanning arm. This construction is necessary in this patent because the implant wheel can be rotated between an implant position with the plane of the wheel substantially vertical and a wafer loading position with the plane of the wheel substantially horizontal, about an axis which is essentially coaxial with the scanning arm. The implant wheel is driven between the loading and implant positions by a motor located outside the vacuum chamber driving a shaft extending through the bellows-type seal.
The use of a bellows-type seal to accommodate the complex motion of the scanning arm relative to the vacuum chamber wall, in the '059 patent, can give rise to problems.
Furthermore, in the '059 patent, the angle of tilt of the implant wheel relative to the ion beam during implantation can be set to provide a desired angle of implantation. This is achieved by manually adjusting the rotational position relative to the tilt axis of the entire scanning arm and drive mechanism. The bellows-type seal must also accommodate this motion.
It is an object of the present invention to provide improved ion implantation apparatus which enables the angle of tilt of the implant wheel to be set remotely and which provides all the facilities of known implantation apparatus with improved sealing arrangements and simpler and more reliable construction.